A TiAl intermetallic compound (also simply referred to as TiAl) is known as light material with heat resistance. TiAl is preferable as material for parts of a missile and parts of an aerospace engine which are required to be light and heat-resistant, for example. When TiAl is used as the material for such parts, there is a case that TiAl needs to be joined. In that case, a joining portion is required to have high-temperature strength equal to a TiAl base material.
As a method of obtaining a joining portion having high-temperature strength equal to a TiAl base material, diffusion bonding is mainly used since welding is not applicable. In the diffusion bonding, a heating temperature, a heating time, a pressure applying method, magnitude of an applied pressure, presence of an insert material and so on are set as parameters. For example, Japanese Patent Publication JP Heisei 4-367382A (Patent Document 1) discloses a high-strength TiAl joined body and a joining method thereof. FIG. 1A and FIG. 1B are schematic views showing a TiAl joining method according to the conventional technique. FIG. 1A shows a joining method according to Japanese Patent Publication JP Heisei 4-367382A and FIG. 1B shows a joining method according to a conventional technique at the time of applying the Japanese Patent Publication JP Heisei 4-367382A. In the joining method in FIG. 1B, diffusion bonding is performed by applying pressure to TiAl intermetallic compounds 101 while heating the TiAl intermetallic compounds 101 with heaters 102. On the other hand, in the joining method in FIG. 1A, metal Ti 103 is used as an insert material, which is different from FIG. 1B, when diffusion bonding is performed by applying pressure to TiAl intermetallic compounds 101 while heating the TiAl intermetallic compounds 101 with heaters 102.
As a related technique, Japanese Patent JP 3459138B (Patent Document 2; corresponding to U.S. Pat. No. 5,863,670(A)) discloses a TiAl intermetallic compound joined body and a manufacturing method thereof. The manufacturing method of the TiAl intermetallic compound joined body is characterized in that: an insert material of which a main component is a mixture of metal phases containing Al and Ti as major elements is positioned to a faying surface of two base materials of a TiAl intermetallic compound and are heated in a temperature range where the insert material become a TiAl intermetallic compound such that reaction synthesis joining is performed; and after the reaction synthesis joining process, heat treatment is performed in which the joined body is held in a temperature range of Ta to (Tα−100) degrees Celsius (Tα is a temperature at which a γ-phase is precipitated from a α-phase) for a predetermined time, or heat treatment is performed in which the joined body is heated to the temperature of (Tα+100) to Tα degrees Celsius and further held in a temperature range of Tα to (Tα−100) degrees Celsius for a predetermined time, when the base materials contain mixed structure of γ-phase equiaxed grains and a lamellar structure having alternately-laminated plate-like γ grains and plate-like α2 grains.
As mentioned above, it is necessary to actively apply pressure to TiAl as shown in FIG. 1A and FIG. 1B, in order to obtain good joining property (e.g. joint strength equivalent of a base material) when diffusion bonding of TiAl is performed. This is because surfaces of TiAl to be joined need to closely come into contact with each other. Here, pressure to be required can be reduced to some extent by inserting an insert material (Ti, and Al and Ti) (Japanese Patent Publication JP Heisei 4-367382A and Japanese Patent JP 3459138B.